Across
- 5. Amount of time it takes for half of the radioactive atoms to decay
- 8. Glaciers cover a large amount of Earth's surface
- 10. Large divisions of time
- 12. Lighter elements join together to create heavier elements
- 14. When Earth gets hotter or colder then it is today
- 17. When the star starts to run out of fuel
- 18. Continents locked close together
Down
- 1. What the universe was formed by
- 2. A rock's age compared to the ages of other rocks around it
- 3. Smaller divisions of time
- 4. Looked at edges of continents
- 6. When a large number of a species disappears in a short amount of time
- 7. How to tell if object is moving towards or away from us
- 9. How to tell how long a star will live
- 11. Wisconsin Episode, 75,000 years ago
- 13. Exact number of years since the rock formed
- 15. When the universe began to cool
- 16. Very large span of time